The present invention relates to a reflection screen for image projection which can be easily produced and exhibits high contrast of projected images, and a method for producing it. The images projected on the reflection screen are easy to view even in a lighted place.
Reflection screens having reflecting property for reflecting light from projectors and light diffusing property for diffusing the reflected light are used as projection screens for OHPs, slide projectors, film projectors and the like.
The most commonly used reflection screens are those comprising a black lining sheet laminated with a white polyvinyl chloride sheet as a light-reflecting substrate. Also used are reflection screens comprising a light-reflecting substrate applied with a white ink containing a pearl pigment or aluminum paste pigment and optionally surface roughened to have fine projections and depressions and thus improve its reflectance.
However, these reflection screens are produced with no consideration to improving the contrast ratio of dark image portions in black and bright image portions in white. Their use is therefore limited to dark places such as a dark room. Attempts have therefore been made to develop reflection screens which improve the contrast of projected images so that clear images can be seen even in a space where ceiling lights and/or natural light from windows may be present. See, for example, Japanese Patent Unexamined Application Publication Nos. Sho 62-229122 and Hei 6-82915.
Japanese Patent Unexamined Application Publication No. Sho 62-229122 discloses a projection screen comprising a transparent plate covering a diffusion surface for diffusing projected light. The transparent plate has numerous small surface portions provided with opaque layers so that the opaque layers do not cut the light paths of diffused light directed to the observer.
Japanese Patent Unexamined Application Publication No. Hei 6-82915 discloses a reflection screen comprising a screen substrate, a reflection layer provided on the substrate and composed of applied white ink and light-absorbing layers composed of light-absorbing ink applied by, for example, printing on the reflection layer surface at numerous portions.
The light-absorbing ink is an ink having a light-absorbing peak wavelength of around 575 nm and showing reddish black hue.
However, the production of the reflection screen according to Japanese Patent Unexamined Application Publication No. Sho 62-229122 requires a molding operation to provide the numerous small surfaces on the transparent plate. In addition, it is extremely troublesome to form opaque layers only in the small surfaces not present on the light paths of diffused light directed to the observer. Therefore, when a large reflection screen is produced by this technique, it disadvantageously leads to low productivity and high cost.
Further, according to Japanese Patent Unexamined Application Publication No. Hei 6-82915, the specific light-absorbing ink is defined so as not to absorb the projected light of bright images in white, thereby improving the contrast. However, since the light-absorbing layer does not have sufficient thickness to adequately absorb ambient light, for example, indoor illumination light, dark images in black are also brightened in a lighted environment. On the other hand, it is possible to make the dark images sharp by increasing the area of the light-absorbing layers, but this in turn makes the bright images in white become grayish. Thus, sharp images with high contrast still cannot be obtained.
Accordingly, the object of the present invention is to solve the above problems, i.e., to provide a reflection screen for image projection which can be produced easily at low cost, show good contrast of projected images and hence make projected images sufficiently visible even in a lighted space, and a method for producing it.